Display Alert message after File download in ASP.Net

Sir good morning

I have made a function where I am exporting data into excel and it is working fine but after successful export data alert message in not displaying.

please help me.

CS

protected void BtnExportReport_Click(object sender, EventArgs e)
{
    if (TxtStockDate.Text == "")
    {
        MessageTitle = "Select Date";
        MessageSwalTitle = "Oops !!!";
        MessageSwalDisplay = MessageTitle;
        MessageSwalType = "warning"; // info , success , warning , error
        ScriptManager.RegisterStartupScript(this, this.GetType(), "Script", "FunctionAlertMessage('" + MessageSwalTitle + "', '" + MessageSwalDisplay + "', '" + MessageSwalType + "');", true);
        return;
    }

    //if (RbtnListReport.SelectedIndex < 0)
    //{
    // MessageTitle = "Report Option Not Selected";
    // MessageSwalTitle = "Oops !!!";
    // MessageSwalDisplay = MessageTitle;
    // MessageSwalType = "warning"; // info , success , warning , error
    // ScriptManager.RegisterStartupScript(this, this.GetType(), "Script", "FunctionAlertMessage('" + MessageSwalTitle + "', '" + MessageSwalDisplay + "', '" + MessageSwalType + "');", true);
    // return;
    //}

    //if (RbtnListReport.SelectedIndex == 0)
    //{
    // ReportOption = "BLOCKED";
    // ExportReport();
    // //ExportReportBlockedList();
    //}
    //else if (RbtnListReport.SelectedIndex == 1)
    //{
    // ReportOption = "UNBLOCKED";
    // //ExportReportBlockedList();
    // ExportReport();
    //}

    BtnExportReport.Enabled = false;
    ExportReport();
    BtnExportReport.Enabled = true;

    ClientScript.RegisterClientScriptBlock(this.GetType(), "alert", "swal('Success!','Report Downloaded Successfully' , 'success')", true);
    return;
}
// End Btn Export

protected void ExportReport()
{
    try
    {
        // SET DATABASE CONNECTION.
        ConnectionStringFunction();
        SqlCn = new SqlConnection(ConPath);
        SqlCn.Open();

        List<SqlParameter> sqlParameterExport = new List<SqlParameter>();
        DateTime DateTimeStart = DateTime.ParseExact(TxtStockDate.Text, "MM/dd/yyyy", null); // textbox show be read only =false
        DateTimeStart = Convert.ToDateTime(DateTimeStart, System.Globalization.CultureInfo.GetCultureInfo("hi-IN").DateTimeFormat);
        //"hi-IN" is culture information about India. You can change as per culture like French, German, etc.

        //DateTime DateTimeEnd = DateTime.ParseExact(TxtEndDate.Text, "MM/dd/yyyy", null); // textbox show be read only =false
        //DateTimeEnd = Convert.ToDateTime(DateTimeEnd, System.Globalization.CultureInfo.GetCultureInfo("hi-IN").DateTimeFormat);
        ////"hi-IN" is culture information about India. You can change as per culture like French, German, etc.

        FromDate = DateTimeStart.ToString("MM/dd/yyyy");
        //ToDate = DateTimeEnd.ToString("MM/dd/yyyy");

        sqlParameterExport.Add(new SqlParameter("MainCompanyCode", int.Parse(TxtUserCompanyCode.Text)));
        sqlParameterExport.Add(new SqlParameter("@Date", FromDate));

        SqlDt = new DataTable();
        SqlCm = new SqlCommand("ReportVehicleStock", SqlCn);
        SqlCm.CommandType = CommandType.StoredProcedure;

        if (sqlParameterExport.ToArray().Length > 0)
        {
            SqlCm.Parameters.AddRange(sqlParameterExport.ToArray());
        }
        SqlDa = new SqlDataAdapter(SqlCm);
        SqlDa.Fill(SqlDt);

        //// CALCULATE RUNNING TOTAL (WILL DISPLAY AT THE FOOTER OF EXCEL WORKBOOK.)
        //Decimal dTotalPrice = 0;
        //for (int i = 0; i <= SqlDt.Rows.Count - 1; i++)
        //{
        // //dTotalPrice += SqlDt.Rows[i].Field<Decimal>(1); // 1 is cell no
        //}

        // NOW ASSIGN DATA TO A DATAGRID.
        DataGrid dg = new DataGrid();
        dg.DataSource = SqlDt;
        dg.DataBind();

        // THE EXCEL FILE.
        string sFileName = "VehicleStock_" + System.DateTime.Now + ".xls";
        sFileName = sFileName.Replace("/", "");

        // SEND OUTPUT TO THE CLIENT MACHINE USING "RESPONSE OBJECT".
        Response.ClearContent();
        Response.Buffer = true;
        Response.AddHeader("content-disposition", "attachment; filename=" + sFileName);
        Response.ContentType = "application/vnd.ms-excel";
        EnableViewState = false;

        ////======================
        //StringBuilder sb = new StringBuilder();
        //sb.AppendLine("AAAAAA");
        //sb.AppendLine("BBBBBB");
        //Response.Write(sb.ToString());
        ////======================

        System.IO.StringWriter objSW = new System.IO.StringWriter();
        System.Web.UI.HtmlTextWriter objHTW = new System.Web.UI.HtmlTextWriter(objSW);

        dg.GridLines = GridLines.Both;
        dg.HeaderStyle.Font.Bold = true; // SET EXCEL HEADERS AS BOLD.
        dg.HeaderStyle.BackColor = System.Drawing.Color.LightBlue;
        dg.RenderControl(objHTW);

        //style to format numbers to string
        string style = @"<style> .textmode { mso-number-format:\@; } </style>";
        Response.Write(style);

        string ReportTitle = "<table><tr><td> <style> font-size:medium; color:blue </style> <b>" + "Report Name : " + "Vehicle Stock as on " + DateTimeStart.ToString("dd/MMM/yyyy") + "</b></td> </tr></table>";
        string ReportDate = "<table><tr><td> <style> font-size:medium; color:blue </style> <b>" + "Report Date : " + System.DateTime.Now.ToLongDateString() + "</b></td> </tr></table>";
        string ReportTime = "<table><tr><td> <style> font-size:medium; color:blue </style> <b>" + "Report Time : " + System.DateTime.Now.ToShortTimeString() + "</b></td> </tr></table>";

        // ADD A ROW AT THE END OF THE SHEET SHOWING A RUNNING TOTAL OF PRICE.
        Response.Write(ReportTitle);
        Response.Write(ReportDate);
        Response.Write(ReportTime);

        // STYLE THE SHEET AND WRITE DATA TO IT.
        Response.Write("<style> TABLE { border:solid 1px #999; } " +
        "TD { border:solid 1px #D5D5D5; text-align:left; } </style>");

        //Response.Write("<style> TABLE { border:dotted 1px #999; } " +
        // "TD { border:dotted 1px #D5D5D5; text-align:left; } </style>");
        Response.Write(objSW.ToString());

        //// ADD A ROW AT THE END OF THE SHEET SHOWING A RUNNING TOTAL OF PRICE.
        //Response.Write("<table><tr><td><b>Total: </b></td><td></td><td><b>" +
        // dTotalPrice.ToString("N2") + "</b></td></tr></table>");

        Response.End();
        dg = null;

        MessageTitle = "Report Successfuly Downloaded";
        TransactionStatus = true;

    }
    catch (Exception ex)
    {
        //MessageTitle = "Transaction Successful \\n\\Job Card No : " + TmpDocumentNo.Trim() + " Generated";
        TransactionStatus = false;
        //SqlTran.Rollback();
        MessageTitle = "Transaction Failed !!!!" + "<br/>" + ex.Message.ToString();
    }
    finally
    {
        SqlCn.Close();
    }
    //End Finally
    // ========================= End Try
}